The invention relates to random access memory for data storage. More specifically, the invention relates to a magnetic random access memory device including an array of memory cells and circuitry for writing data to the memory cells.
Magnetic Random Access Memory ("MRAM") is a type of non-volatile memory that is being considered for long term data storage. Accessing data from MRAM devices would be orders of magnitude faster than accessing data from conventional long term storage devices such as hard drives. Additionally, the MRAM devices would be more compact and would consume less power than hard drives and other conventional long term storage devices.
A typical MRAM device includes an array of memory cells. Word lines extend along rows of the memory cells, and bit lines extend along columns of the memory cells. Located at a cross point of a word line and a bit line, each memory cell stores a bit of information as an orientation of a magnetization. The magnetization orientation of each memory cell will assume one of two stable orientations at any given time. These two stable orientations, parallel and anti-parallel, represent logic values of "1" and "0." The magnetization orientation of a selected memory cell may be changed by supplying current to a word line and a bit line crossing the selected memory cell. The currents create magnetic fields that, when combined, can switch the magnetization orientation of the selected memory cell from parallel to anti-parallel or vice versa.
All of the other memory cells along the word and bit lines crossing the selected memory cell will hereinafter be referred to as "half-selected" memory cells. In order to switch the magnetization orientation of only the selected memory cell, all of the half-selected memory cells should be unaffected by the currents flowing through the word and bit lines crossing the selected memory cell.
A need exists to reduce the chances of half-selected memory cells being inadvertently switched; otherwise, the memory array will be gradually erased as bits are written into the array. Reducing this inadvertent switching will make MRAM devices more reliable.
A need also exists to reduce power consumption of MRAM devices, especially MRAM devices for portable applications such as notebook computers and digital cameras. Batteries supply the current to the word and bit lines during write operations. Reducing power consumption would extend battery life.